This invention relates to a hydraulic drill unit for drilling multimaterial, thick layer stock.
The U.S. Pat. to Rieger et al., No. 3,259,023, discloses a drilling machine wherein the feed and speed rates are varied during the drilling operation.
Most portable drilling equipment for difficult materials or large diameter holes have fixed feed rates and a limited range of speed variations. The feed rates are set for the most difficult materials in the stack. Speed variations to accommodate different materials in the stack have been very difficult and unreliable from hole to hole if the stack thicknesses and material varied since the finite position of the drill point relative to the original drill length and position in the stack is difficult to ascertain.
New drill units have been developed that have the capability to change both speed and feed rates, but the problem of determining precisely when and how much to change from hole to hole for varying conditions still remains.